How to get the pressure force applied on an object?
A force field object can not be edited using nodes.
Nodes are reserved for materials.

I am guessing you want to animate the force within to simulate increasing wind force. You can do this by selecting your wind force and opening up the physics tab. 



In this tab hover the strenght attribute and press 'i' to insert a keyframe.
Than place another keyframe somewhere else on your timeline to animate the wind force. Same can be done for the other attributes.